so the threshold can now be based on the GimpHistogramChannel enum.
Add a channel menu to the threshold dialog and a channel argument to
the PDB procedure (which is new in 2.10).
If I hadn't forgotten what the "RGB" channel is supposed to do I would
have implemented the RGB mode in GimpOperationThreshold correctly.
Right now I'm just guessing. Anyone?
- don't include <gdk-pixbuf/gdk-pixbuf.h> in headers in app/
- instead, include it in many .c files instead of <glib-object.h>,
finally acknowledging the fact that app/ depends on gdk-pixbuf almost
globally
- fix up includes as if libgimpbase depended in GIO, which it soon will
